all: Remove usage of deprecated io/ioutil (#7971)

As of Go 1.16 io/ioutil is deprecated. This replaces usage with the
corresponding functions in package os and package io.

lib/logger/logger.go

@@ -10,7 +10,6 @@ package logger
 import (
 	"fmt"
 	"io"
-	"io/ioutil"
 	"log"
 	"os"
 	"strings"
@@ -75,7 +74,7 @@ func New() Logger {
 	if os.Getenv("LOGGER_DISCARD") != "" {
 		// Hack to completely disable logging, for example when running
 		// benchmarks.
-		return newLogger(ioutil.Discard)
+		return newLogger(io.Discard)
 	}
 	return newLogger(controlStripper{os.Stdout})
 }

lib/logger/logger_test.go

@@ -6,7 +6,7 @@ package logger
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"log"
 	"strings"
 	"testing"
@@ -186,12 +186,12 @@ func TestControlStripper(t *testing.T) {
 }
 
 func BenchmarkLog(b *testing.B) {
-	l := newLogger(controlStripper{ioutil.Discard})
+	l := newLogger(controlStripper{io.Discard})
 	benchmarkLogger(b, l)
 }
 
 func BenchmarkLogNoStripper(b *testing.B) {
-	l := newLogger(ioutil.Discard)
+	l := newLogger(io.Discard)
 	benchmarkLogger(b, l)
 }